As metal oxide semiconductor field effect transistor (MOSFET) devices are shrinking and moving towards 3-dimensional (3D) structures, such as FinFETs, it is becoming increasingly difficult to use ion implantation to tune the device threshold voltage (Vth). An alternative method to tune the Vth is to use different metals with varying work functions as the gate material in a high-k metal gate (HKMG) structure. In planar device structures the metal gate is typically deposited using physical vapor deposition (PVD), but as device dimensions are shrinking and becoming 3D, atomic layer deposition (ALD) will become necessary to deposit the metal gate in a conformal manner. Metals and compounds such as tantalum-silicon-nitride, ruthenium, tantalum carbide, molybdenum nitride, and titanium aluminide with band-edge work functions have been evaluated as candidates to be used as gate p- and n-metals in MOSFET devices. For Multi-Vth integrated circuit (IC) devices, materials with mid-gap work functions are also desired. Nickel silicide, titanium silicide, hafnium carbide, and hafnium aluminide have been found to possess mid-gap work functions. Many of the metal gate materials have been deposited using PVD. However, it is difficult to tune the work function of these materials when deposited using PVD techniques.
Therefore, there is a need to develop new materials and methods for deposition for advanced work function materials used in advanced IC devices.